Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient's facial appearance, especially in instances where the teeth are noticeably crooked or where the jaws are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion during mastication.
One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient's teeth and an arch wire is placed in the slot of each bracket. The arch wire forms a track to guide movement of teeth to desired locations.
The ends of orthodontic arch wires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an arch wire is provided for each of the patient's upper and lower dental arches. The brackets, buccal tubes and arch wires are commonly referred to collectively as “braces”.
In many types of orthodontic techniques, the precise position of the appliances on the teeth is an important factor for helping to ensure that the teeth move to their intended final positions. In general, orthodontic appliances that are adapted to be adhesively bonded to the patient's teeth are placed and connected to the teeth by either one of two techniques: a direct bonding technique, or an indirect bonding technique.
In the direct bonding technique, the appliance and adhesive are grasped with a pair of tweezers or other hand instrument and placed by the practitioner on the surface of the tooth in an approximate desired location. Next, the appliance is shifted along the surface of the tooth as needed until the practitioner is satisfied with its position. Once the appliance is in its precise, intended location, the appliance is pressed firmly onto the tooth to seat the appliance in the adhesive. Excess adhesive in areas adjacent the base of the appliance is removed, and the adhesive is then allowed to cure and fix the appliance firmly in place. While the direct bonding technique described above is in widespread use and is considered satisfactory by many, there are shortcomings that are inherent with this technique. For example, access to surfaces of malposed teeth may be difficult. In some instances, and particularly in connection with posterior teeth, the practitioner may have difficulty seeing the precise position of the bracket relative to the tooth surface. Additionally, the appliance may be unintentionally dislodged from its intended location during the time that the excess adhesive is being removed adjacent the base of the appliance.
Indirect bonding techniques avoid many of the problems associated with direct bonding. In general, indirect bonding techniques known in the past have involved the use of a placement device or transfer apparatus having a shape that matches the configuration of one or more of the patient's teeth in the dental arch. One type of placement device or transfer apparatus is often called a “transfer tray” and typically has a cavity for receiving a number of teeth simultaneously. A set of appliances such as brackets are releasably connected to the tray at certain, predetermined locations.
During the use of an orthodontic transfer apparatus for indirect bonding, an adhesive is typically applied to the base of each appliance by the orthodontist or a staff member. The device is then placed over the patient's teeth and remains in place until such time as the adhesive hardens. Next, the apparatus is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the apparatus are now bonded to respective teeth at their intended, predetermined locations.
In more detail, one method of indirect bonding of orthodontic appliances using the transfer tray described above includes the steps of taking an impression of each of the patient's dental arches and then making a replica plaster or “stone” model from each impression. Next, the appliances are bonded to the stone models at desired locations. Optionally, the brackets may be adhesive precoated brackets.
The transfer tray is then made by placing a matrix material over the model as well as over the appliances placed in the model. For example, a plastic sheet matrix material may be held by a frame and exposed to radiant heat. Once the plastic sheet material has softened, it is placed over the model and the appliances. Air in the space between the sheet material and the model is then evacuated, and the plastic sheet material assumes a configuration that precisely matches the shape of the replica teeth of the stone model and attached appliances. The plastic sheet matrix material is then allowed to cool and harden to form a tray. The tray and the appliances (which are embedded in an interior wall of the tray) are then detached from the stone model. If the cured adhesive that was used to bond the appliances to the stone model remains on the base of the appliances after detachment from the stone model, the adhesive serves as a “custom” base having a concave contour that precisely replicates the convex contour of the previous attachment location of the stone model, as well as the convex configuration of the intended mounting location of the appliances on the patient's teeth.
Once the patient has returned to the practitioner's office, a quantity of adhesive is placed on the base of each appliance, and the tray with the embedded appliances is then placed over the matching portions of the patient's dental arch. Since the configuration of the interior of the tray closely matches the respective portions of the patient's dental arch, each appliance is ultimately positioned on the patient's teeth at precisely the same location that corresponds to the previous location of the same appliance on the stone model.
Indirect bonding techniques offer a number of advantages over direct bonding techniques. For one thing, and as indicated above, it is possible to bond a plurality of appliances to a patient's dental arch simultaneously, thereby avoiding the need to bond each appliance in individual fashion. In addition, the transfer apparatus helps to locate the appliances in their proper, intended positions such that adjustment of each appliance on the surface of the tooth before bonding is avoided. The increased placement accuracy of the appliances that is often afforded by indirect bonding techniques helps ensure that the patient's teeth are moved to their proper, intended positions at the conclusion of treatment.
In recent years, many improvements have been made in the field of indirect bonding. However, there is a continuing need in the art to improve methods for fabricating the transfer apparatus or transfer tray. For example, improper fit of the transfer tray over the patient's teeth is a common problem. For example, when a practitioner utilizes an indirect bonding technique, it is critical that the practitioner be able to precisely place the transfer tray over matching surfaces of the patient's teeth. An improperly fitted transfer tray may result in appliances being bonded to locations on the patient's teeth that are imprecise and do not correspond to the previous location of the same appliance on the stone model. As a result, malpositioned teeth may move to unintended positions during the treatment program.
Although the transfer tray is fabricated to match the surfaces of the patient's teeth, as is often the case, the transfer tray may be somewhat unstable, loose, or inaccurate. Such instability can result from several factors. For example, inaccuracies may arise during the steps leading up to the fabrication of the transfer tray. Inaccuracies may arise during fabrication of the impression of the patient's teeth, or during the fabrication of the stone model based upon each impression. Inaccuracies may also arise during bonding of the appliances to the stone model at desired locations. Additionally, inaccuracies may arise due to the fact that the transfer tray is customarily fabricated of a material that is insufficiently rigid. Due to any one or a combination of the foregoing factors, a certain amount of instability, “wiggle”, or “play” often arises when the transfer tray is placed over matching surfaces of the patient's teeth during the indirect bonding process. The potential for such instability increases, especially when the transfer tray is arranged for placement over only a small number of teeth, e.g., two or three teeth.
For the foregoing reasons, it is desirable to increase placement accuracy of the transfer tray over matching surfaces of the patient's teeth during the indirect bonding procedure. It would be desirable to provide a transfer tray that includes a feature or mechanism that would provide stabilization and enable the practitioner to visually assess or determine whether the transfer tray has been placed or seated onto the patient's teeth in the position as originally planned and intended. Other than its surfaces that match a patient's teeth, currently available transfer trays (made for one or multiple teeth) do not provide the practitioner with such a feature or mechanism.